1. Technical Field
This invention relates generally to endoluminal devices and, more specifically, to a stent having an integral sealing ring.
2. Background of the Invention
A stent is an elongated device used to support an intraluminal wall. Stents may also have a prosthetic graft layer of fabric or covering lining the inside or outside thereof, such a covered stent being commonly referred to in the art as an intraluminal prosthesis, an endoluminal or endovascular graft (EVG), or a stent-graft. A prosthesis may be used, for example, to treat a vascular aneurysm by removing the pressure on a weakened part of an artery so as to reduce the risk of rupture. Stents and prostheses are typically introduced into a lumen in a compressed state and expanded to an expanded state by self-expansion, balloon-expansion, or a combination thereof.
Various stent architectures are known in the art, including filamentary and cut tube architectures. Braided and wound architectures are subclasses of architectures within the filamentary class of architectures. Included among the braided filamentary stent architectures are those described in U.S. Pat. No. 4,655,771 to Hans I. Wallsten and incorporated herein by reference. The '771 Wallsten patent is only one example of many variations of braided stents known in the art, however, and thus not intended as a limitation of the invention described herein later. Braided stents tend to be very flexible, having the ability to be placed in tortuous anatomy and still maintain patency. This flexibility of braided stents make them particularly well-suited for treating aneurysms in the aorta, where often the lumen of the vessel becomes contorted and irregular both before and after placement of the stent.
As used herein, flexibility or stiffness can be described in terms of the amount of force required to bend a stent into an arc. The force required to bend a tubular stent of a particular length into a given arc having a central angle and a given arc radius, is a measure of the stent flexibility. Thus, comparing two stents of equal length with different stent architectures, the stent requiring greater force to bend it into a given arc is relatively stiffer, whereas the stent requiring lesser force is relatively more flexible. It is not uncommon for a stent to be installed in a lumen that is somewhat tortuous in nature. In such cases, there is a need for the prosthesis to be flexible or bendable without kinking, especially in the region where the stent is inflected in its deployed configuration.
One disadvantage of braided stents is typically that the radial strength on the end of the braided stent may be substantially less than the radial strength in the middle of the stent. As used herein, “radial strength” can be described generally as the resistance of a stent to radial compression. A stent with more radial strength exerts a greater outward radial force when compressed than does a stent with less radial strength. Insufficient radial strength on the stent ends may result in an incomplete seal or migration of the device after implantation.
An incomplete seal between the outer wall of the prosthesis and the inner wall of the lumen may allow intraluminal fluid to leak between the prosthesis and the lumen wall. Similarly, an incomplete seal between the outer wall of a first modular stent component and the inner wall of a second modular stent component may allow intraluminal fluid to leak between the mating modular components or relative movement of the two stent components. Such leaks, sometimes referred to as an “endoleaks,” may cause a number of problems including fatality, for patients experiencing such leaks. Thus, it is desirable to provide a prosthesis that minimizes the potential for endoleaks.
Various designs have been proposed to minimize endoleaks. For example, U.S. patent application Ser. No. 09/327,069, filed Jun. 7, 1999, by Staudenmeier et al. assigned to the assignee of this invention, and incorporated herein by reference, describes one modular stent embodiment wherein interfacing components have interlocking, hourglass-shaped ends to provide a fluid-tight seal. The teachings of this application, however, are not specific to any particular type of stent architecture. U.S. patent application Ser. No. 09/442,165, filed Nov. 16, 1999, by Chouinard et al., also assigned to the assignee of this invention and incorporated herein by reference, discloses overcoming typically decreased radial strength at the ends of braided stents by configuring the end portion as a wound architecture.
Stents having one or more elevations of greater diameter than the rest of the stent structure have also been proposed as having a number of benefits, including having increased radial strength in the elevations. Such designs are particularly known with respect to braided stent architectures. U.S. Pat. No. 5,575,818 to Pinchuk, U.S. Pat. No. 5,725,547 to Chuter, and U.S. Pat. No. 5,993,483 to Gianotti, all incorporated herein by reference, discuss braided stents having such elevations.
There is still a need in the art, however, for additional methods for fabricating braided stents with elevations, as well as a need for braided stent structures that incorporate elevations and other radial-strength-increasing attributes in their design to minimize endoleaks.